It is well established that DARPP-32 is a key integrator of striatal signaling in physiological conditions as well as in the context of psychostimulants. Beside dopamine, various neurotransmitters such as glutamate act on and modify DARPP-32 downstream signaling. Our studies have demonstrated the importance of multiple signaling pathways converging on DARPP-32 in the action of drugs of abuse, and recently we have developed state-of-the-art technologies proving that these signaling events are specifically regulated in different sub-populations of medium spiny neurons (MSNs) that differentially express Dl and D2 types of dopamine receptor. Our ongoing research will focus on studies of mGluRS, an important GPCR invovled in glutamate-dependent DARPP-32 regulation, and two kinases, CKI and CK2. CKI is a crucial player in the mGluR5/DARPP-32 pathway and CK2 is essential for regulation of DARPP-32 nuclear trafficking. We have generated novel mouse lines for each of the three proposed Aims that will allow us not only to study the impact of psychostimulants in vivo but also to evaluate the relative importance of D1- and D2-MSNs in these phenomena. To address these questions we propose three Aims in Project 2 of the Program Project Grant. In Aim I we will study the role of the newly discovered mGluRS regulator Norbin in the actions of psychostimulants. In Aim II we will study the role of CK1 in the mGluRS/DARPP-32 pathway in vivo. We will also further charcterize the CK16 over expressing mice that present some behavioral features that ressembles ADHD. We will further address differences observed between Dl and D2 receptor pathways. In Aim III we will study the role of CK2 in the actions of psychostimulants, in both Dl and D2-MSNs using specific KO strategies. Results from this Project will complement the other two Projects of this Program Project grant. In addition we will also carry out a number of collaborative studies with Projects 1 and 3, including studies involving spine morphology with Project 1 and phosphoproteomic studies and behavioral studies with Project 3.